XmAddTabGroup man page

This function is obsolete and its behavior is replaced by setting XmNnavigationType to XmEXCLUSIVE_TAB_GROUP. When the keyboard is used to traverse through a widget hierarchy, primitive or manager widgets are grouped together into what are known as tab groups. Any manager or primitive widget can be a tab group. Within a tab group, move the focus to the next widget in the tab group by using the arrow keys. To move to another tab group, use KNextField or KPrevField.

Tab groups are ordinarily specified by the XmNnavigationType resource. XmAddTabGroup is called to control the order of traversal of tab groups. The widget specified by tab_group is appended to the list of tab groups to be traversed, and the widget's XmNnavigationType is set to XmEXCLUSIVE_TAB_GROUP.